Ultrafiltration is a membrane based filtration process of industrial and biological significance used to separate, purify and concentrate macromolecular solutions. In human physiology, the kidney performs ultrafiltration of blood through biological membranes located in nephrons, the functional units of the kidney. A related important application of ultrafiltration (using synthetic membranes) is to replace diseased kidney function using Renal Replacement Therapy (RRT) in patients suffering from Acute Renal Failure and End-stage-Renal Disease. Synthetic membranes are used to perform ultrafiltration in the food, water purification and pharmaceutical industries to name a few applications.
The replacement of renal function in persons with renal failure by dialysis is dependent on the ability to filter out waste products while preserving metabolically costly proteins, peptides and cells. Thus, there exists a need to maximize the retention of a large macromolecular solute of interest in the feed (supply) solution, and more specifically to improve the selectivity of current ultrafiltration systems. Examples of macromolecules of interest in this discussion are synthetic and natural proteins, carbohydrates, nucleic acids etc. with molecular dimensions of the order of and larger than 1 nm. Specifically, the retention of serum albumin in blood during ultrafiltration together with the clearance of middle molecules like β2-microglobulin is not satisfactorily addressed in conventional therapies.
Diffusive transport of a molecule from one point in the fluid to another is proportional to the difference of concentrations of the molecule between the two points and is approximately inversely proportional to the molecular size, up to sizes excluded by the membrane. Thus, smaller molecules are extracted from, for example, blood more quickly than larger ones.
Conventional renal function replacement therapies often include membranes that have poor selectivity toward biologically important molecules or are too large for the possibility of patient implantation. The definition of membranes includes filtration devices utilizing well-defined pores as well as those utilizing a matrix of fibers. The former category includes membranes for industrial and therapeutic ultrafiltration and high flux dialysis; the latter category includes gels for gel permeation chromatography, the glomerular basement membrane and other extracellular matrices.